According to the known art, triaryl phosphates are prepared by a process in which POCl.sub.3 is reacted with the appropriate phenol at elevated temperatures in the presence of large amounts of AlCl.sub.3 as a catalyst. Examples of triaryl phosphates to which the present invention is directed are tricresyl, triphenyl, phenylcresyl and phenyl-i-propylphenyl phosphates. Triaryl phosphates have a number of industrial applications, such as plasticizers for polymers, fire retardants, lubricant oil additives and hydraulic fluids.
The processes of the art, however, present several severe drawbacks. Firstly, HCl evolves as a waste product, and the process, among other common disadvantages of acid evolution, requires that glass-lined vessels be employed. Secondly, only relatively low conversions--of up to about 88%--are usually obtained. Thirdly, aromatic by-products are wasted and, together with the large amounts of catalyst employed, form wastes which are burdensome and must be disposed of, because of environmental hazards.
Replacing POCl.sub.3 by H.sub.3 PO.sub.4 potentially solves part of the above-mentioned problems, since the intermediates resulting from the reaction can be recycled, the corrosion problem is eliminated because AlCl.sub.3 is not used, and no HCl evolves, and there is essentially no waste. This replacement, however, leads to impractically slow reactions which are not useful from an industrial point of view.